1. Field of the Invention
The present invention relates to a thin film magnetic head and a method of manufacturing the same, and more particularly to a composite type thin film magnetic head constructed by stacking an inductive type thin film writing magnetic head and a magnetoresistive type reading magnetic head one on the other and a method of manufacturing such a composite type thin film magnetic head.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. In order to improve a performance of a reading magnetic head, a reproducing head utilizing a magnetoresistive effect has been widely used. As the reproducing magnetic head utilizing the magnetoresistive effect, an AMR reproducing element utilizing a conventional anisotropic magnetoresistive (AMR) effect has been widely used. There has been further developed a GMR reproducing element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than the normal anisotropic magnetoresistive effect by several times. In the present specification, these AMR and GMR reproducing elements are termed as a magneto-resistive reproducing element or MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits per a unit square inch has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes and is still small in size.
A height of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. This height is generally called MR Height, here denoted by MRH. The MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
At the same time, a performance of a recording head is also required to be improved. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a pole portion at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining a performance of an inductive type thin film writing magnetic film is a throat height TH. This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible.
FIGS. 1-12 show successive steps of a known method of manufacturing a conventional typical thin film magnetic head and a completed magnetic head. This magnetic head belongs to a composite type thin film magnetic head which is constructed by stacking an inductive type thin film writing magnetic head and a magnetoresistive type thin film reading magnetic head one on the other. In a practical process of manufacturing the thin film magnetic head, a number of thin film magnetic heads are simultaneously formed on a single wafer, and therefore end faces of respective magnetic heads do not appear. However, for the sake of explanation, the end face is shown in the drawings.
At first, as illustrated in FIG. 1, on a substrate 11 made of an electrically insulating and non-magnetic material such as aluminum-titan-carbon (AlTiC), is deposited an insulating layer 12 made of alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m. Then, as depicted in FIG. 2, after forming a bottom shield layer 13 constituting a magnetic shield for the MR reproducing magnetic head and having a thickness of about 3 .mu.m on the insulating layer, an insulating layer 14 is formed by depositing an alumina with a thickness of 100-150 nm as shown in FIG. 3.
As illustrated in FIG. 3, on the insulating layer 14, is formed a magnetoresistive layer 15 having a thickness of several tens nanometers (nm) and being made of a material having the magnetoresistive effect, and the magnetoresistive layer is shaped into a desired pattern by a precise mask alignment. Next, as represented in FIG. 4, an alumina insulating layer 16 like as the alumina insulating layer 14 is formed by sputtering to have a thickness of 100-150 nm, and then a magnetic layer 17 made of a permalloy and having a thickness of 3-4 .mu.m is formed on the alumina insulating layer as shown in FIG. 5. This magnetic layer 17 serves not only as an upper shield layer for magnetically shielding the MR reproducing element together with the above mentioned bottom shield layer 13, but also as a bottom magnetic layer of the inductive type writing thin film magnetic head to be manufactured later. Here, for the sake of explanation, the magnetic layer 17 is called a first magnetic layer, because this magnetic layer constitutes one of magnetic layers forming the thin film writing magnetic head.
Next, as shown in FIG. 6, on the first magnetic layer 17, is formed a gap layer 18 made of a nonmagnetic material such as alumina to have a thickness of about 150-300 nm by sputtering. An electrically insulating photo-resist layer 19 is formed on the write gap layer 18 and is shaped into a desired pattern by a highly precise mask alignment. On the photo-resist layer there is formed a first thin film coil layer 20 made of, for instance copper.
Next, as illustrated in FIG. 7, an electrically insulating photo-resist layer 21 is formed on the first thin film coil layer 20 by an highly precise mask alignment, and then the photo-resist layer is baked at, for instance 250.degree. C. in order to flatten its surface. On the thus flattened surface of the photo-resist layer 21, is formed a second thin film coil layer 22 and a photo-resist layer 23 is formed on the second thin film coil layer 22 by a highly precise mask alignment. Then, the photo-resist layer 23 is baked at, for instance 250.degree. C. such that its surface is flattened as shown in FIG. 8. A reason for forming the photo-resist layers 19, 21 and 23 with a highly precise mask alignment as stated above is that the throat height TH and MR height MRH are defined on the basis of edge positions of these photo-resist layers.
Next, as illustrated in FIG. 9, on the gap layer 18 and photo-resist layers 19, 21 and 23, a second magnetic layer 24 made of a permalloy and having a thickness of 3-4 .mu.m is selectively formed in accordance with a desired pattern. This second magnetic layer 24 is brought into contact with the first magnetic layer 17 at a position remote from the magnetoresistive layer 15, and the thin film coils 20, 22 pass through a closed magnetic path constituted by the first and second magnetic layers. A pole portion of the second magnetic layer 24 is formed into desired shape and size which define a track width. Furthermore, an overcoat layer 25 made of alumina is formed on exposed surfaces of the second magnetic layer 24 and gap layer 18 by sputtering. Finally, a side wall 26 at which the magnetoresistive layer 1 is formed is polished to form an air bearing surface (ABS) 27 as depicted in FIG. 10, said air bearing surface opposing to a record medium. During the formation of the air bearing surface 27, the magnetoresistive layer 15 is also polished to obtain an MR reproducing element 28. In this manner, the above mentioned throat height TH and MR height MRH are determined by the polishing. In an actual manufacturing process, contact pads for establishing electrical connections to the thin film coils 20, 22 and MR reproducing element 28 are formed, but these contact pads are not shown in the drawings.
FIGS. 10, 11 and 12 are cross sectional, front and plan views, respectively showing the known composite type thin film magnetic head manufactured in the above explained manner, while the overcoat layer 25 is dispensed with. It should be noted that in FIG. 10, the alumina insulating layers 14 and 16 surrounding the MR reproducing element 28 are denoted by a single insulating layer, and in the plan view of FIG. 12, the thin film coil 22 is denoted to have a concentric shape for the sake of simplicity. As clearly shown in FIG. 10, an angle .theta. between a straight line S connecting side edges of the photo-resist layers 19, 21 and 23 isolating the thin film coil 20, 22 and an upper surface of the second magnetic layer 24 is called an apex angle. This apex angle is one of important factors for determining a property of the thin film magnetic head together with the throat height TH and MR height MRH. Furthermore, as shown in the plan view of FIG. 12, a width W of the pole portion 24a of the second magnetic layer 24 is small. A width of tracks recorded on a record medium is determined by said width W, and therefore it is necessary to make this width W as small as possible in order to realize a high surface recording density.
As explained above, in order to improve the surface recording density on the magnetic record medium, it is necessary to improve a performance of the thin film recording magnetic head comprising the first and second magnetic layers 17 and 24, gap layer 18 and thin film coil 20, 22. In the composite type thin film magnetic head having the reading magnetic head using the magnetoresistive element and the thin film recording magnetic head stacked one on the other, it is necessary to improve the performance of the writing magnetic head as well as the reading magnetic head. In order to improve the performance of the writing magnetic head, it is important that the throat height TH and apex angle .theta. shown in FIG. 10 should be formed accurately such that they are not deviated from desired design values. However, in the known manufacturing method, it is difficult to control these parameters precisely and to manufacture the magnetic head in accordance with desired design values. That is to say, the throat height TH is defined by a distance from the air bearing surface 27 to an edge of the insulating layer 19 for isolating the thin film coil 20, 22, said edge opposing to the pole portion 24a of the second magnetic layer 24. However, in an actual manufacturing process, a position of said edge of the insulating layer 19 could not be clearly defined, and the air bearing surface 27 is polished on the basis of a throat height zero position defined by the edge position under an assumption that said edge would be formed at a desired position. During the formation of the thin film coil 20, 22, the heating process is carried out at about 250.degree. C., and the photo-resist layer constituting the insulating layer is melt and a pattern of the insulating layer is varied. Therefore, a position of said edge of the insulating layer is deviated from a desired position, and thus a value of the throat height TH which corresponds to a length of the pole portion 24a and is determined by using a position of the edge of the insulating layer as a positional reference might be deviated from a desired design value. Particularly, when the photo-resist layers constituting the insulating layers 19, 21 and 23 are formed to have a large thickness, said deviation in the pattern might amount to a very large value such as about 0.5 .mu.m. Therefore, a fine throat height TH of several micron meters to sub-micron meters could never be attained with a high reproducibility. Further, in case of using such a thick photo-resist layer, a desired pattern might be deviated by an unevenness in a thickness. For instance, in a composite type thin film magnetic head for a high frequency, a throat height TH has to be made not larger than 1.0 .mu.m. The above mentioned deviation of 0.5 .mu.m is very large and a number of defective throat heights TH are produced to decrease a manufacturing yield and a manufacturing cost is increased.
During the above mentioned heating process, the photo-resist film of the insulating layers 19, 21 and 23 is melt, and therefore a profile defined by side walls of these insulating layers as shown in FIG. 10 is varied and the apex angle .theta. is also varied. The apex angle .theta. influences the performance of the thin film magnetic head and the deviation in the apex angle might sometimes cause a defect in the property of the thin film magnetic head. In this manner, in the known method of manufacturing the thin film magnetic head, it is difficult to improve the performance of the writing magnetic head. Such a problem would be manifest in accordance with a progress in miniaturization of the thin film magnetic head.
The above explained demerit of the known method of manufacturing the thin film magnetic head is mainly due to the deviation in pattern of the photo-resist film caused by the process of heating the photo-resist film during the formation of the thin film coil 20, 22, but this process is inevitable for flattening the surface of the insulating layer and isolating the coil windings.
Furthermore, although the performance of the reading magnetic head can be improved by using a GMR reproducing element having a high sensitivity as the magnetoresistive element, in order to further increase a surface recording density, it is necessary to manufacture the magnetic head such that the MR height MRH defined by a height of the element measured from the air bearing surface 27 should not be deviated from a desired design value. In an actual manufacturing, the MR height MRH is determined by an amount of polishing the air bearing surface 27 like as the throat height TH, and this polishing is carried out while a position of the edge of the insulating layer is used as a positional reference. Since a position of the edge of the insulating layer is varied by the heating process as stated above, the MR height MRH is also varied and could not be formed to have a desired design value. Therefore, a manufacturing yield is decreased by the variation in the MR height MRH, and a manufacturing cost is increased.
Particularly, in a composite type thin film magnetic head including the writing magnetic head and the reading magnetic head having the magnetoresistive element stacked one on the other, a balance between the throat height TH of the writing magnetic head and the MR height MRH of the reading magnetic head has to be taken into consideration. These two factors are determined by a positional relationship of the insulating layers 19, 21 and 23 made of photo-resist, a precision in the mask alignment of the MR reproducing element and a precision in the polishing process for forming the air bearing surface. Therefore, a pattern alignment of the insulating layers 19 and 21 with respect to the MR layer 15 should be carried out with a minimum error. However, although this error could be minimum, there is still an error due to the deformation in a pattern of the photo-resist which constitutes the insulating layers 19, 21 and 23 isolating the coil windings of the thin film coil 20, 22 by the heating process, and thus the throat height TH and MR height MRH contain an error. Then, a balance between the writing magnetic head and the reading magnetic head is broken and it is no more possible to manufacture a composite type thin film magnetic head having a superior performance.
Moreover, as can be seen from FIG. 11, if a width of the first magnetic layer 17 and a width W of the pole portion 24a of the second magnetic layer 24 near the air bearing surface differ greatly from each other, there might be produced a leakage of a magnetic flux called a side fringe magnetic flux. Particularly, in the composite type thin film magnetic head having the recording thin film magnetic head and the MR reproducing head 28 formed integrally, the first magnetic layer 17 also serves as the magnetic shield for the MR reproducing head, a width of the first magnetic layer has to be inherently larger than a width W of the pole portion 24a of the second magnetic layer 24, and therefore there might be induced a relatively large side fringe magnetic flux. When such a side fringe magnetic flux is produced, an undesired side write phenomenon might occur and an effective width of a record track is increased. In accordance with a recent progress in the high surface recording density, a track width has been shortened. but when the above mentioned side write occurs, there might be produced a cross talk between adjacent tracks as well as an accidental erase of a magnetization pattern recorded in adjacent tracks, so that a sufficiently high surface recording density could not be realized.
In order to solve the above problems, there has been proposed to construct the trim structure by forming a protruded portion 17a in the first magnetic layer 17 as shown in FIG. 13 and this protruded portion is formed to have a width identical with a width of the pole portion 24a of the second magnetic layer 24. Such a solution has been described in Japanese Patent Application Laid-open Publications, Kokai Hei 7-220245, 7-225917 (corresponding to U.S. Pat. No. 5,438,747) and 7-296331.
Upon forming the protruded portion 17a in the first magnetic layer 17 shown in FIG. 13, in order to match a width of the protruded portion to a width of the pole portion 24a of the second magnetic layer 24, after forming the pole portion of the second magnetic layer, an ion beam etching, for instance an ion milling is performed while the pole portion of the second magnetic layer is used as a mask to remove the gap layer 18 and a portion of the first magnetic layer 17 is removed over a part of its thickness, for instance over about 500 nm. However, an etching rate of the ion milling for an alumina constituting the gap layer 18 is low such as about 30 nm/minute, and therefore a long processing time is required and a through-put is liable to be decreased.
Furthermore, an etching rate of the ion milling for a permalloy constituting the second magnetic layer 24 is high such as 200 nm/minute, and thus a thickness of the second magnetic layer 24 has to be larger by considering a reduction in thickness during the etching process. The second magnetic layer 24 is formed by a plating, and therefore if a thickness of the magnetic layer is larger, it is required to use a thick photo-resist film which is used for forming the pole portion 24a in accordance with a given pattern. When a thickness of the photo-resist film is large, it is difficult to narrow a width W of the pole portion 24a, and a pole portion having a width of an order of sub-micron meters could not be formed any more.
In order to form the protruded portion 17a having the same dimension as that of the pole portion 24a of the second magnetic layer 24 by etching the gap layer 18 and first magnetic layer 17 with the ion milling, while the pole portion 24a of the second magnetic layer 24 is used as a mask, an ion beam has to be made incident substantially at right angles. However, the ion milling is performed at right angles, debris of etched material might adhere to side walls of the protruded portion 17a of the first magnetic layer 17 and pole portion 24a of the second magnetic layer 24. By means of such adhered substances, the first and second magnetic layers 17 and 24 might be magnetically short-circuited and an effective track width might be increased. Therefore, the thin film magnetic head having a desired performance could not be attained.